Dingwell, Donald B.; Knoche, Ruth; Webb, Sharon L.; Pichavant, Michel
The effect of B2O3 on the viscosity of haplogranitic liquids.
In: American Mineralogist, Vol. 77, Nr. 5-6: S. 457-461
The effect of B2O3 on the viscosity of a haplogranitic liquid (KrO-Na,O-AlrOr-SiO,) has
been determined at I atm pressure in the temperature interval of 600-1600 °C. Viscosity
measurementso f a haplogranite, haplogranite + 4.35 wt% B2O3 and haplogranite + 8.92 wt% B2O3 have been performed using the concentric cylinder and micropenetration methods.
The viscosity of a B-enriched natural rhyolite obsidian, macusanite from Macusani,
Peru, has also been determined.
The viscosity of haplogranite liquid decreases with the addition of B2O3 at all temperatures
investigated. The viscosity decrease is nonlinear, with the strongestd ecreasee xhibited
at low B2O3 concentration. The temperature dependence of the viscosity of all the
investigated liquids is Arrhenian, in strong contrast to the case for B2O3 Iiquid. The Arrhenian
activation energy is much lower in the B2O3-bearing liquids than in the B2O3-free
haplogranite, with the result that the effect of B2O3 on viscosity is a strong function of
temperature. At temperatures corresponding to the crystallization of B-rich granitic and
pegmatitic systems the addition of I wt% of B2O3 decreases the viscosity 2 orders of
magnitude. The macusanite liquid exhibits a reduced viscosity compared with B-free rhyolite
that is consistent with the synthetic liquid systematics. B must be considered as a
fluxing agent in B-rich granitic and pegmatitlc systems.